Kishor Mehta

The second international intercomparison on EPR tooth dosimetry

Eighteen international EPR laboratories participated in the second intercomparison programme. Each participant had to prepare enamel samples and evaluate the absorbed dose from molars that were irradiated in vitro in the range 0-1000 mGy. The objective of the programme was to bring together all methods which are currently applied by different laboratories for EPR dose reconstruction and to demonstrate the present state of dosimetry. An overview of the essential features of the different methods is presented. The current accuracy of EPR tooth enamel dosimetry under defined conditions of irradiation is evaluated

STERILE INSECT TECHNIQUE: A MODEL FOR DOSE OPTIMIZATION FOR IMPROVED STERILE INSECT QUALITY

Abstract The sterile insect technique (SIT) is an environment-friendly pest control technique with application in the area-wide integrated control of key pests, including the suppression or elimination of introduced populations and the exclusion of new introductions. Reproductive sterility is normally induced by ionizing radiation, a convenient and consistent method that maintains a reasonable degree of competitiveness in the released insects. The cost and effectiveness of a control program integrating the SIT depend on the balance between sterility and competitiveness, but it appears that current operational programs with an SIT component are not achieving an appropriate balance. In this paper we discuss optimization of the sterilization process and present a simple model and procedure for determining the optimum dose.

Alanine-ESR dosimetry for radiotherapy IAEA experience

At present, the most commonly used transfer dosimeters for radiotherapy applications are TL dosimeters. They are being used for intercomparison between SSDLs (about 70) and the IAEA dosimetry laboratory. However, there are some undesirable characteristics of this dosimetry system. We have a study in progress at the IAEA to evaluate the alanine-ESR system as an alternative to TLDs. There are several desirable qualities which make alanine an attractive dosimeter. Preliminary data suggest that the alanine-ESR dosimetry system has the potential to replace TLDs for intercomparison amongst SSDLs in the therapy-level dose region.

High-dise standardization service of the IAEA

Abstract The mandate of the International Atomic Energy Agency (IAEA) includes assistance to Member States to establish nuclear technologies safely and effectively. In pursuit of this, the International Dose Assurance Service (IDAS) was initiated as a key element of the high-dose standardization program of the IAEA. The standardization of dosimetry for radiation processing provides justification for the regulatory approval of irradiated products and their unrestricted international trade. In recent times, the IAEA dosimetry laboratory has expended considerable effort in establishing a quality assurance program for its transfer dosimetry used for the IDAS.

Reference dosimeter system of the iaea

Abstract Quality assurance programmes must be in operation at radiation processing facilities to satisfy national and international Standards. Since dosimetry has a vital function in these QA programmes, it is imperative that the dosimetry systems in use at these facilities are well calibrated with a traceability to a Primary Standard Dosimetry Laboratory. As a service to the Member States, the International Atomic Energy Agency operates the International Dose Assurance Service (IDAS) to assist in this process. The transfer standard dosimetry system that is used for this service is based on ESR spectrometry. The paper describes the activities undertaken at the IAEA Dosimetry Laboratory to establish the QA programme for its reference dosimetry system. There are four key elements of such a programme: quality assurance manual; calibration that is traceable to a Primary Standard Dosimetry Laboratory; a clear and detailed statement of uncertainty in the dose measurement; and, periodic quality audit.

Dose distribution in electron-irradiated PMMA: effect of dose and geometry

Abstract Depth-dose distributions for an electron beam are generally determined with either a stack irradiation geometry or a wedge (generally with an angle of about 50°–60°) made from an electrically-conducting material (such as, aluminium) or a non-conducting material (such as, PMMA). If the non-conducting wedge is thicker than the electron range, the stored charge in the material could influence the measured depth-dose distribution. This effect was investigated for 7-MeV electrons for PMMA with the wedge angle varying from 0° to 60°. The maximum-to-surface dose ratio was used as a characteristic parameter of the shape of the distribution. The depth-dose distribution measured by a dosimetry film placed inside the wedge-pair was similar to the standard shape when the wedge angle was larger than about 55° (dose ratio ∼1.5). However, as the angle was decreased, this ratio sharply increased almost linearly up to about 15°, and then leveled off at about 3. We also studied the effect of the surface dose on this dose ratio for the wedge angle of 0°, where we found that the ratio increased with the dose. Both of these effects can be explained by the presence of the electrostatic field around the dosimetry film due to stored charge in the non-conducting PMMA.

Temperature stabilization of alanine dosimeters used for food processing and sterilization

The International Atomic Energy Agency has established a dose quality audit service for radiation processing facilities. The objective of the service is to provide an independent check on the routine dosimetry system in use at the facility. The audit service is based on the use of alanine EPR dosimetry. Generally, alanine dosimeters are irradiated at the facility together with a product, and the response is then analyzed at the IAEA laboratory. Practice of the audit service has shown that the main uncertainty in alanine dosimetry is due to absence of temperature control at the irradiation facilities. Here, a method for stabilizing the temperature of the dosimeter during irradiation is proposed.

Dose distribution in polyethylene irradiated with A 10-MeV electron beam

Abstract Radiation modification of the gel content and the complex modulus of plastics was used to determine the depth-dose distribution in a solid polyethylene block irradiated with a 10 MeV electron beam, under typical radiation processing conditions. The results indicate that the accumulated charge has no significant effect on the shape of the dose profile. This suggests that, under certain circumstances, intrinsic “dosimeters” could be more appropriate than conventional thin film dosimeters placed inside the material for dose measurements in electrically non-conducting materials.

Measurements of electron depth-dose distributions in thick plastics and effects of accumulated charge

Abstract Depth-dose distributions in PMMA and polyethelene for a 10 MeV electron beam under typical radiation processing conditions were measured using radiochromic films. Due to the accumulated charge, the measured depth-dose distribution depends strongly on irradiation geometry. Also, the extent to which the observed distribution is affected depends on material, its radiation history and absorbed dose.